5-fluorouracil (hereinafter sometimes referred to as “5-FU”) and its derivatives (such as tegafur, carmofur, and doxifluridine) are fluorouracil drugs that are most widely used as anticancer drugs at present.
5-FU is degraded and inactivated mainly by the actions of a series of pyrimidine metabolizing enzymes in the pyrimidine metabolic pathway in the liver. Specifically stated, as shown in FIG. 1, 5-FU administered to the body is metabolized first into 5-fluoro-dihydrouracil (hereinafter sometimes referred to as “FDHU”) by the action of dihydropyrimidine dehydrogenase (hereinafter sometimes referred to as “DPD”), which is the first enzyme in the pyrimidine metabolic pathway; and then into fluoro-β-ureidopropionic acid (hereinafter sometimes referred to as “F-β-UPA”) by the action of dihydropyrimidinase (hereinafter sometimes referred to as “DHPase”), which is the second enzyme in the pyrimidine metabolic pathway; and then into fluoro-β-alanine (hereinafter sometimes referred to as “F-β-alanine”) and carbon dioxide (final metabolites) by the action of β-ureidopropionase (hereinafter sometimes referred to as “β-UPase”; which is the third enzyme in the pyrimidine metabolic pathway.
It has been reported that about 80% of 5-FU administered to the body is degraded in the pyrimidine metabolic pathway (Cancer (Phila), 68, 499-501, 1991), and that DPD (first enzyme) is the rate-limiting enzyme in this metabolic pathway (Cancer Res., 47: 2203-2206, 1987). Accordingly, the administration of 5-FU or another fluorouracil drug to a subject with DPD deficiency or DPD activity reduction is likely to result in abnormally high fluorouracil drug concentration in the blood, thus causing severe side effects (e.g., myelosuppression, digestive symptoms, or the like), because the fluorouracil is not normally metabolized (Cancer Inves. 11 (2): 239-240, 1993). Further, it is known that DPD activity greatly varies individually, and is also different between the sexes (J. Clin. Oncol., 12: 2248-2253, 1994; Adv. Exp. Med. Biol., 431: 811-816, 1998).
Thus, in Europe and America, the necessity of diagnosing the existence, nonexistence, or degree of pyrimidine metabolic disorder, especially a pyrimidine metabolic disorder caused by DPD deficiency and DPD activity reduction, in an individual subject. is urged, to prevent the side effects of 5-FU and other fluorouracil drugs.
There is an established DPD deficiency diagnosis method, wherein the DPD activity of peripheral blood mononuclear cells is determined (Cancer Res., 53: 5433-5438, 1993; Phermacogenetics. 4: 301-306. 1994; J. Inherited. Metab. Dis., 16: 574-576, 1993). However, the method is not suitable for diagnosing cancer patients, who are the subjects to be given fluorouracil drugs, since the method involves use of radioactive substances and complicated pretreatment.
Recent progresses in genetic analysis techniques have facilitated diagnosis of DPD gene deficiency. Further, a number of reports have been made on polymorphism of the DPD gene, which may cause DPD activity reduction. However, the correlation between the DPD gene polymorphism and DPD activity has not been elucidated yet. Thus, it is extremely difficult to assess the existence or nonexistence of DPD activity, in particular the degree of DPD activity, on the basis of the genetic information.
In the present situation where fluorouracil drugs have proved effective in anticancer therapy and are often enhanced by a variety of drugs that inhibit the enzymatic activity of DPD (a metabolizing enzyme for fluorouracil drugs), there is a demand for the development of a simple method for diagnosing the pyrimidine metabolic capacity, i.e., the existence, nonexistence, or degree of pyrimidine metabolic disorder, in a subject beforehand, to predict and prevent the side effects that may be caused by fluorouracil drug therapy.